GCC -> EGCS
EGCS (Experimental/Enhanced GNU Compiler System, pronounced “eggs”) was a forked from GCC in 1997 and was re-merged in April 1999.
By 1991, GCC 1.x had reached a point of stability, but architectural limitations prevented many desired improvements, so the Free Software Foundation started work on GCC 2.x. But during the mid-1990s, the FSF kept such close control on what was added to the official version of GCC 2.x that GCC was used as one example of the “cathedral” development model by Eric S. Raymond.
XFree86 -> Xorg-X11